The invention relates to a valve assembly comprising a flow control valve having a piston displaceable in a bore against a biasing force of a spring, and a discharge throttle.
It is known to use a valve assembly, which comprises a flow control valve, in e.g., a steering pump of a motor vehicle for providing a uniform oil flow to an actuator connected with the steering pump. Controlling the oil flow to the actuator is especially important during a rapid drive on a highway, when the requirement in power assist is insignificant and, therefore, the power assist requires small amount of oil, but when, in case of a suddenly flattened tire, a large amount of oil need be delivered to the actuator to insure an adequate steering. Accordingly, it was suggested to use so-called main or discharge throttles for controlling the oil flow. The discharge throttle is provided in the working conduit leading to the actuator and should insure a constant oil flow to the actuator. The discharge throttle is used together with a slide valve for providing a predetermined oil flow. The drawback of this arrangement consist in that the slide valve should have a predetermined minimal play for enabling its displacement. However, this minimal play leads to leakage losses and, thus, reduces the hydraulic efficiency of the pump. These leakage losses are especially noticeable during idle running of the pump when the pump supplies a small amount of oil.
Accordingly, the main object of the invention is a valve assembly of the above-discussed type which would insure an easy flow control, while substantially reducing leakage losses.